The Cooperative Breast Cancer Registry will provide investigators with archival pathological material to use in their investigations of predictive factors and diagnostic markers. Previous work has been hampered by limited resources of case material and/or inadequate measures of outcome. A Cooperative Registry, by combining several large sources of material into a single entity following a common protocol, should serve to advance this important work. This application is a response from Kaiser Permanente, Northwest Region (KPNW), a pre-paid health plan in the Portland, Oregon metropolitan area in continuous existence since World War II. KPNW has provided comprehensive medical care to an increasing population since that time. All members have a single Health Record into which all medical information is routinely entered. All computer systems at KPNW are interlinked electronically. Further, all encounters of each member are linked by the unique Health Record number, a system that facilitates collection of comprehensive information about Health Plan members. The KPNW Department of Pathology has available more than 3800 invasive breast cancer specimens diagnosed since 1975. In addition to the actual pathological specimens, KPNW possesses accurate outcome data from its own Tumor Registry and comprehensive medical care information in each patient's Health Record. The combination of pathological and clinical resources, coupled with commitment to and experience in research make KPNW an excellent resource for the Cooperative Breast Cancer Registry.